Polyhydroxybutyric acid (PHB) is a kind of biopolymer produced by microorganisms. As a microbially degradable thermoplastic resin, it is expected to serve as a material that can be applied to a wide range of fields such as pharmaceuticals, agricultural chemicals, medical materials, and industrial materials. PHB is a kind of polyhydroxyalkanoic acid (PHA), and is a polyester synthesized from acetyl-CoA via three-step reactions. Various methods of microbial production of PHA have so far been disclosed. For example. Patent Document 1 discloses a production method of PHB. However, all of those methods have their drawbacks in terms of requiring an organic carbon source as the assimilable carbon source.
Under the foregoing circumstances, various methods of efficient microbial production of PHA without requiring a reducing substance of an organic carbon source have been searched for. Although a number of studies on blue-green algae PHA have so far been reported, a locally increased enzyme activity has been shown not to result in an increase in the amount of PHA (Non Patent Document 1). In order to further increase the amount of PHA, the carbon metabolism needs to be drastically modified to drive the metabolic flow toward PHA. However, it has also been shown that modification of individual metabolic enzymes does not lead to the modification of the entire metabolism. Further, although the inhibition of sugar catabolism by the clock protein gene is reported in blue-green algae belonging to genus Anabaena, the algae do not have the ability to produce PHA, and thus there has been no report about the utilization of the algae in a production of PHA (Non Patent Document 2).
Among other organic acids, particularly succinic acid and lactic acid are known as raw materials of plastics, and from the environmental as well as economic points of view, there has been a demand for the establishment of a biological production system of these acids. While succinic acid is mainly synthesized from petroleum, recently startup companies engaged in a bio-based production of succinic acid have been established abroad. In light of this, inexpensive, environmentally-friendly production technology of succinic acid will directly bring benefits to society. According to the conventional method, succinic acid is produced through fermentation by heterotrophic bacteria using plant-derived carbohydrates. Meanwhile, there is concern about the stable supply of plant-derived carbohydrates due to their competition with food, unsettled weather, price hike, and so on.